In recent decades, advances in modem chemistry and more sophisticated instrumentation have led to a plethora of clinical tests. However, the equipment and the trained personnel needed to perform such tests led also to an increase in costs. To cut down on the costs related to clinical diagnosis, many physicians frequently outsource testing of blood and other specimens to centralized or specialized laboratories. Outsourcing clinical diagnostics, however, often increases the time between acquiring a sample and obtaining a test result. A delay in obtaining a test result is especially disadvantageous when time is a critical factor in differential diagnosis, for example, in the treatment of heart attacks, poisoning or strokes. Furthermore, a delay in obtaining test results adds to the overall cost.
The time span between acquiring a sample and obtaining a test result is not only of paramount importance in clinical diagnosis, but also in a variety of other fields. Such fields are, for example, environmental chemistry to detect a source of pollution, military field tests to detect poisonous gases, or criminological investigation to find traces of chemical markers. Time constraints, as well as the requirement to perform diagnostic tests at the place of sample collection led to the development of compact, self-contained test systems. Such self-contained test systems may be categorized into two different classes.
The first class may be characterized as qualitative test systems. Many qualitative test systems provide all required reagents, and a sample can be analyzed without further need of instrumentation. In U.S. Pat. No. 3,726,645 to Kaezmarek et al., U.S. Pat. No. 3,713,779 to Sirago et al., and U.S. Pat. No. 3,689,224 to Agnew et al., for example, small, flat hand-held test kits are described, in which a liquid or gaseous sample reacts with reagents provided by the test kit. A color change of an indicator reveals the presence of analyte. In these test kits, manual application of pressure is usually used to move and mix reagents; and the sample. In other test systems, for example in U.S. Pat. No. 4,806,316 to Johnson et al., the sample is propelled by gravity or a pressure difference. Again, a color change indicates the presence of analyte. In a further example, U.S. Pat. No. 4,859,421 to Apicella, additional elements in a test kit are described, such as one-way valves that allow only unidirectional flow of reagents. Furthermore, additional reagents for positive and negative controls may be provided.
The second class may be characterized as quantitative test systems. Quantitative test systems generally require a specialized instrument, commonly a photometer or fluorimeter. Such quantitative test systems utilize various ways of detection and various ways of how the sample is moved within the test device. In U.S. Pat. No. 4,963,498 to Hillmant et al., for example, a test system is described in which a blood sample is mixed with a reagent and subsequently drawn by capillary action into a flow path. Interactions between the reagents and the sample cause a change in flow rate. The flow rate is measured using a photocell, and the change in the flow rate is then correlated with the concentration of the analyte. In another example, U.S. Pat. No. 3,799,742 to Coleman describes a test system in which a sample is placed into a small test container. The sample is then manually pushed through a filter unit into a cuvette, where a color reaction takes place. The small test container is subsequently inserted into a reading device and the concentration of the analyte is calorimetrically determined. In U.S. Pat. No. 4,673,657 to Christian, a sample is placed into an assay card and forced to a detection zone by a roller bar. A pulse vacuum may firer move the sample repeatedly over the detection zone. The detection zone may specifically bind up to 250 analytes, and the analytes can then be automatically detected and quantified via an optical or magnetic detector.
Although various quantitative and qualitative test systems are known in the art, almost all test systems have a number of disadvantages. Typically, the assays performed in such systems are single-step assays, i.e., one sample is mixed with one reagent or set of reagents, and the result of the reaction is then measured. However, many modem diagnostic reactions employ multiple steps prior to the detection reaction, for example reduction of a sample to liberate disulfide bound thiols, or coupled enzymatic reactions to indirectly measure an analyte or secondary reactions for signal amplification.
Another disadvantage of many quantitative and qualitative test systems is that reaction of a sample with a substrate, and detection of the analyte, occur in the same location. This often poses problems when additional processing steps are required after the addition of reagents to the sample. Where samples are moved from one location to another within a test system, reproducible test conditions may be difficult to achieve.
Yet another disadvantage of known quantitative and qualitative test systems is that many of them utilize squeezable containers for storage and dispensing of reagent solutions. Despite the simple operation of squeezable containers, dispensing an accurate and precise amount of a reagent from a squeezable container is often problematic. Moreover, when an accurate and precise flow rate of a reagent is needed, squeezable containers may produce inaccurate and non-reproducible results.
Yet further, while many test systems are supplied with appropriate amounts of reagents, and typically follow relatively simple protocols, a problem frequently persists in that the accuracy and precision of test results become operator i.e. technique dependent. Such measurement is therefore often prone to errors.
Thus, many test systems are known in the art to qualitatively and quantitatively determine the presence of an analyte in a sample. However, current test systems tend to limit the complexity of a reaction sequence with which an analyte can be determined. Surprisingly, despite a growing number of new and useful diagnostic systems, there is no test system that permits a relatively quick and simple detection of an analyte in a sample that requires complex test procedures, without using sophisticated instruments. Therefore, there is still a need for methods and test systems that overcomes these limitations.